Four smallmouth bass streams in the Potomac River watershed are compared. In the largest stream, the Shenandoah River near Berryville, Virginia, the fingerling bass (Micropterus dolomieu) grew to an average length of 4.25 inches during 1936, whereas in the South Branch of the Potomac near Romney, West Virginia, fingerlings attained a length of 2.75 inches by the end of the summer. In the Shenandoah River and probably also in its North Fork, bass grow rapidly and attain the legal size of 10 inches in three years, but in the South Branch of the Potomac and in the Cacapon River from four to six years or more are required for the fish to grow to legal size. The muddy condition of the Shenandoah and North Fork for long periods during the summer affects the success of natural propagation. These streams also have extensive riffle areas over limestone ledges where bass find shelter while feeding. In the South Branch of the Potomac and in the Cacapon River the riffles are short and little shelter is available.